German authorities urged 15,000 more people to flee their homes in a city on the swollen Elbe river as central Europe's worst floods in a decade also threatened Hungary after causing havoc in the Czech Republic and Austria.

The daring rescue of an elderly woman from a flooded river in Missouri is caught on video.

DCI

The river Danube reached a new record high in Budapest but the Hungarian capital's mayor sought to ease concerns, saying water levels were stabilising, although about 1,200 people were evacuated along the river.

Budapest has averted the worst of the floods that caused devastation elsewhere in central Europe, as flood defences held firm, with the Danube starting to recede early Monday.

"We have no reports of any catastrophic situation, the situation is normalizing," Budapest Mayor Istvan Tarlos told a joint press conference with Hungarian Prime Minister Viktor Orban early Monday.

The deluge has also sparked massive emergency responses in Austria and Slovakia.

A torrent of flood waters in Germany has turned vast areas into a brown water world, sparked a mass mobilisation of emergency workers and caused billions of euros in damage in what one lawmaker termed a "national catastrophe".

Rescue helicopters criss-crossed the sky and military armoured personnel carriers rumbled through the flood zone, where thousands of troops, firefighters and volunteers were frantically building up flood defences with sandbags.

Across central Europe, the floods have killed at least 18 people, including 10 in the Czech Republic.

The German city of Magdeburg urged 15,000 residents to leave the east bank of the river Elbe, where an almost 7.5 metre (24 feet) peak -- up from the normal level of two metres -- was expected to strain saturated dykes for the next few days.

"We hope that the dykes will withstand the pressure over the coming days, but we can't be 100 percent sure," said fire brigade spokesman Andreas Hamann, one of 1,200 emergency staff working around the clock in the area.

The move was described as a precaution, but a city spokesman said "people really are supposed to leave" in face of the danger. In all, 23,000 people in and around the city have been told to evacuate this weekend.

"The hardest thing is not knowing what to do," Brigitte Ilsmann, 88, said as she sat with a group of elderly Germans in a Magdeburg school sports hall turned disaster evacuation centre.

Evacuated from her care home, the old lady who moves with a walker took refuge in the facility where the Red Cross has set up cots with grey blankets and offers thermoses of coffee, baskets full of apples and biscuits.

Soldiers in Magdeburg were also struggling to save a power installation in the harbour area, as water damage would not only knock out electricity to tens of thousands of homes but also to water pumps running at full tilt.